n = int(input())
s = input()
nr = s.count('R')
nw = len(s)-nr
a = ('R'*nr)+('W'*nw)
c = 0
for i in range(n):
  if(s[i:i+1] != a[i:i+1]):
    c += 1
print(c // 2) n = int(input()) n int(input()) int input() input s = input() s input() input nr = s.count('R') nr s.count('R') s.count s count 'R' nw = len(s)-nr nw len(s)-nr len(s) len s nr a = ('R'*nr)+('W'*nw) a ('R'*nr)+('W'*nw) 'R'*nr 'R' nr 'W'*nw 'W' nw c = 0 c 0 for i in range(n):
  if(s[i:i+1] != a[i:i+1]):
    c += 1 i range(n) range n if(s[i:i+1] != a[i:i+1]):
    c += 1 s[i:i+1] != a[i:i+1] s[i:i+1] s i:i+1 i i+1 i 1 a[i:i+1] a i:i+1 i i+1 i 1 c += 1 c 1 print(c // 2) print c // 2 c 2 nw = len(s)-nr len(s)-nr nw nr = s.count('R') s.count('R') nr c = 0 0 c c += 1 1 c n = int(input()) int(input()) n s = input() input() s a = ('R'*nr)+('W'*nw) ('R'*nr)+('W'*nw) a
n = int(input())
s = input()
nr = s.count('R')
nw = len(s)-nr
a = ('R'*nr)+('W'*nw)
c = 0
for i in range(n):
  if(s[i:i+1] != a[i:i+1]):
    c += 1
print(c // 2)